Electrical system for remote transmission of mechanical movements



Oct. 19, 1954 J. R. NlLSON ELECTRICAL SYSTEM FOR REMOTE TRANSMISSION OF MECHANICAL MOVEMENTS 2 Sheets-Sheet 1 Filed April 21, 1955 F/Gi.

WW I.% W 4 WW 5 W a a I V/ 5 an? M 0 fl W W Z Z j fa a 5 z 6 INVENTOR. JOHN E. /V/. so/v 5r MGM Patented Oct. 19, 1954 ELECTRICAL SYSTEM FOR REMOTE TRANS- MISSION OF MECHANICAL MOVEMENTS John R. Nilson, Michigan City, Ind., assignor to The Hays Corporation, Michigan City, Ind, a corporation of Indiana Application April 21, 1953, Serial No. 350,173 8 Claims. (Cl. 318--28) This invention relates to improvements in electrical systems for the remote transmission of mechanical movement, and, more particularly, it relates to such a system employing differential transformers as mechanical-electrical transducers.

The primary object of this invention is to provide a system of this character wherein only three wires are required for the transmission lines of the system, thereby effecting economy of time and materials for the installation of the system over that of other systems requiring four or more wires, and also making possible the installation of the present system in place of obsolete equipment in existing telemetering systems employing three or more wires.

A further object is to provide a system of this character wherein changes in temperature of one of the transducers will not change the ratio of the voltage existing in the primary and secondary circuits, even though such changes in temperature cause a change in resistance of the windings of the transducers and cause a change in the current in the entire system.

A further object is to provide a system of this character which is balanced in the transmission line so that different resistances caused by different lengths of transmission lines in different installations will have no deleterious effect.

A further object is to provide a system of this character employing a differential transformer in which the circuit is so arranged that the output of the transformer is increased as compared to other systems heretofore employed.

Other objects will be apparent from the following specification.

In the drawings:

Fig. 1 is a wiring diagram illustrating one emhodiment of the invention;

Fig. 2 is a wiring diagram illustrating another embodiment of the invention;

Fig. 3 is a detail view of a differential transformer illustrating a modified arrangement;

Fig. 4 is a detail view of another modified arrangement of the transformer; and

Fig. 5 is a detail view of still another modifled form of differential transformer.

Referring to the drawings, and particularly to Fig. 1, the numeral I designates a differential transformer having two primary windings I I and i2 and a single secondary winding IS. A conductor I4 carries primary current to the primary winding II, and a conductor I carries primary current to the primary winding I2. A conductor It connects the two windings II and I2. A

lead I! is tapped at I8 to the conductor IS and is connected to the winding I3. A conductor I9 is also connected with the winding I3 and cooperates with conductor I4 and I5 to constitute the third line of a three-conductor transmission line. The windings II, I 2 and I3 of the differential transformer [G are so arranged that an alternating current passed through the two primary windings II and 42 produces a magnetic flux in each primary winding, and the secondary i so arranged with respect to the two primaries that the combined magnetic flux of the primary winding's produces a net effective flux of Zero in the secondary winding I3.

A shiftable magnetic member 29 is juxtaposed to the windings II, I2 and I3 in such a manner that it may have a neutral or zero position at which the net effective flux in the secondary winding I3 is zero. The member 29, however, may be shifted with respect to the windings II, I2 and I3 in such a manner as to cause an increase in the magnetic coupling of one primary winding with the secondary winding, while decreasing the magnetic coupling of the other primary winding with the secondary winding. Such action results in the production of a variable magnetic flux in the secondary winding I3. The variable magnetic flux in the secondary winding produces a variable voltage whose phase is determined by the predominance of the flux from one primary winding over the flux from the other primary winding when the fluxes are combined within the secondary winding. The mechanical displacement or movement of the magnetic member 23, therefore, produces in the secondary winding I3 of the differential transformer If! a voltage whose magnitude and phase are functions of the direction and extent of the movement of the magnetic member 2!] with respect to a mag netic neutral point at which the coupling of each of the primary windings with the secondary winding produces a net effective flux of Zero within the secondary winding IS.

A second differential transformer 2! similar to the transformer I8 is located at a point remote from the transformer It]. This transformer consists of the primary windings 22 and 23 and the secondary winding 24. A magnetic member 25 is shiftable relative to the various winding 22, 23 and 2A. The primary winding 22 is connected in series in the conductor I i-44; the primary winding 23 is connected in series in the conductor I 5-45; and the secondary winding 24 is connected in series in the conductor I3-Iii'. This arrangement causes the three wires I4-I4',

55-45 and |3I9 constituting the transmission line, to connect the first differential transformer It! with the second differential transformer M in such a manner that the four primary windings M, 2, 22 and 23 are connected in a series loop, using the two conductors l li i and iii-l5 of the transmission line to carry the primary current.

The secondary winding is of the first diiferential transformer it has one end thereof connected by conductor ll with the junction iii of the two primary windings It and i2 oi the transformer id, the other end of the secondary winding i3 bein connected by conductor H) with the secondary winding 2d of the transformer li'in series relation. This arrangement results in the junction :8 of the two primaries of the first dif ferential transformer being at the mid-point of the potential difference existing at the supply terminals 28 with which the conductors il 1' and l5i5 are connected, it being remembered that the electrical characteristics of the primary windings H, 52, 22 and 23 are similar.

A pair of resistors 2'. and 28 of like resistance are connected in series between the conductors ill and [5 adjacent the supply terminals 26. The conductor 19 connected to the secondary winding 2d of the differential transformer 2!, is tapped at 29 at the junction of the two resistors 2'! and 28. An amplifier or rela 3!] is interposed in the line is between the tap 29 and th secondary winding 24 of the transformer 21. The system may be grounded at ill by connection with the conductor 19.

The output leads 32 from the amplifier 3c are connected to a reversible electric member, such as motor 33. This motor has a drive shaft 34 upon which is mounted a cam 35 juxtaposed to and adapted to engage the armature or magnetic member 25 of the second differential transformer 21.

It will be understood. that the second clifierential transformer 21 is so arranged that its movable magnetic member 25 is caused to be moved by the cam 35 or other drive connection with the electric motor 33. In this connection the use of a motor and cam is understood to be illustrative and is not intended to be limiting, as any else-- tro motive means, such as a solenoid, may be emplayed to respond to the output of the amplifier 38 for the purpose of controlling the position of the magnetic member 25. In the operation of the second differential transformer ill the voltage induced in the secondary winding 24 has a magnitude which is a function of the magnitude of the movement of the magnetic member 25 and whose phase is a function of the direction of the movement of the member 25 from a magnetic neutral position, as previously described.

As previously mentioned, the point 8 at which the lead 57 to the secondary winding 13 of the difierential transformer ii! is tapped is at a midpoint of the potential difference existing at the supply terminals 26 by virtue of the fact that the impedances of the primary windings El, E2, 22 and 23 are similar. Similarly, since the resistors 2'5 and 213 ar similar, the tap point 29 for the conductor it is at the mid-point of the potential existing between the supply terminals The secondaries of the two differential transformers are in a series circuit composed of the secondary windings i3 and the third conductor i-i3 of the transmission line, the relay or amplifier 3&3, and a phantom connection between the points it and 29. in reality the so-called phantom consists of the two circuits carrying the primary current, namely ill, 22, it and H, and i5, 23, i5 and respectively; since the Voltage drops in each of these primary current circuits are equal and opposite, and the two conductors i i-i i and -45 are effectively connee-ted in parallel by the center junction H3 or the two primary windings ii and 12 of the first differential transformer i8 and the center tap 29 of the two resistors 22': and 23 across the supply. The voltage between the mid-points i? and 29 is zero and yet the impedance is not infinite and, therefore, a path for electric current exists, and hence a phantom conductor exists between the two points.

It is therefore apparent that the voltage appearing across the input terminals of the amplifier or relay 353 will be th difierence in the voltages between the secondary windings i3 and 24 of the two differential transformers. The amplifier or relay controls the direction or operation of the drive member 33 connected to position the magnetic member 25 of the second transformer 2| in such a manner as to reduce to zero the difference in the voltage at the two secondary windings iii and 2d. Stated difierently, as a change in the position the magnetic member 28 of the first transformer ill unbalances that first transformer so that the output of the secondar winding it thereof is different from the output of the secondary winding 25 or the second transformer 25, that difference is sensed and amplified at 39 and produces operation of the power member 33 for the purpose of Changing the position of the magnetic member 25 to restore the balance between the outputs of the secondary winding I3 and 2 1, or to equalize the output of the two seccndary windings i3 and When such balance or equality is reached, the output of the amplifier or relay 30 is zero and operation of the power member 33 ceases.

The parts will be so correlated that the position or" the magnetic member 2i: bears a known relationship to the position of the movable magnetic m mber 26 or the first transformer iii and this is indicated or recorded, as by indicator 36 associated with shaft 35 Thus the system has transmitted the intelligence of the mechanical position of the member to a remote point accurately and quickly.

One of the advantages of this system is that the voltage change in the system is greater than that which is produced in the secondaries of the differential transformers alone, thus increasing the strength of the signal supplied to the sensing means and amplifier 3Q and improving both the sensitivity and the responsiveness of the system to small changes. This result occurs as follows: The current of the primary circuit is common to all of the four primary windings i i, I2, 22 and 23. The voltages in those four primary windings i 5, i2, 22 and 23 are therefore proportional to the impedances of the respective windings. When the magnetic members 20 and 25 are in the geometric center or at the point at which the magnetic coupling of the primary windings with the secondary winding is equal, the voltage in winding ii is equal to the voltage in winding i2, and the voltage in winding 22 is equal to the voltage in winding 23, since the impedances of the respective windings are equal. Assuming then that the magnetic member as is displaced toward the winding ll, the impedance of the winding H is increased and that of the winding 12 is decreased. This results in the voltage in winding H being greater than the voltage in the winding 12. The difference between the voltages in windings II and I2 is effectively added to the voltage induced in the secondary winding l3. This results in a total voltage in the secondary winding 13 which is greater than that which would be due to the change in the positioning of the magnetic coupling member 20 only. This greater voltage change per unit of displacement serves to reduce possible errors caused by stray magnetic and electric fields. It will be understood that the same voltage relationship described above exists at the receiver transformer 2| so that high sensitivity and accuracy are achieved at all parts of the system, and superior operating results are obtained.

Another embodiment of the system is illustrated in Fig. 2. In this instance a first differential transformer 40 has the primary windings 4| and 42 and the secondary winding 43. A conductor 44 is connected to one end of the primary winding 4|. A lead 45 connects the other end of the primary winding 4!, here shown as the inner end, with the remote or outer end of the other primary winding 42. A lead 46 connects the other or inner end of the winding 42 with the adjacent end of the secondary transformer winding 43. A conductor 41 is tapped to the lead 46 at tap point 48. A conductor 49 extends from the other end of the secondary winding 43. A movable magnetic member 50 is juxtaposed to the windings 4 I, 42, 43 and is shiftable between a position in which the transformer is electrically neutral or balanced, and an unbalanced position.

A second differential transformer 5| has primary windings 52 and 53 and a secondary winding 54. The conductor 44 is connected to the end of the winding 52 opposite to the end at which it is connected to the winding 4!, so that the winding 52 is in series relation to the winding 4|. A lead 55 connects the other or outer end of the winding 52 with the inner end of the winding 53. A lead 56 extends to one terminal 57 of a supply line. The other terminal 57 of that supply line has connection with the conductor 41.

A pair of resistors 53 and 59 are connected in series across the terminals 51. The resistor 58 is a variable resistor and has a slider 60 connected by a lead (ii to an amplifier or relay 62 to provide one input lead for the amplifier. The other input lead to the amplifier constitutes a lead 63 which is connected with a secondary winding 54 and through that winding with the lead 49 and the secondary winding 43. A branch lead 64 extending from the lead 6! is connected to ground at 65.

The output lead 66 from the amplifier 52 extends to a power member, such as a positioning motor 61, whose shaft 63 operates the member 69, here shown as a cam, by means of which the position of the core or magnetic member ill of the second differential transformer 5! is positioned.

One of the characteristics of this embodiment of the invention is that the slider 60 in contact with the variable resistor 58 accommodates adjustment of resistance to produce a voltage drop from terminal 51 to slider 60 to equal the voltage drop in conductor 41 between terminal 51 and point 58. This condition is likely to vary in each installation and may vary from time to time in the same installation, as ambient temperature changes.

This embodiment also possesses the advantage that only the three wires 44, 47 and 49 are required for the transmission to connect the two differential transformers and the other elements of the system. This facilitates the installation of the system with the requirement of a minimum number of wires, and also facilitates the use of the system as a replacement in existing telemetering systems requiring only three wires as is common.

Another advantage of the Fig. 2 embodiment, as well as the Fig. 1 embodiment, is that changes in temperature in any one of the differential transformers will not materially change or unbalance the system. The effect of any such temperature changes will be to change the resistance of the primary windings and, consequently, to change the current in the entire system, but it will not change the ratio of the voltage existing in the primary and secondary circuits. Since this is a mill-balance system, such variations of resistance are of no consequence.

In the Fig. l embodiment, another advantage is that there is no change in the operation of the system responsive to changes in the lengths of transmission lines in different installations. It will be apparent that any change of this character, that is, an increase in resistance due to increase in the length of transmission lines, adds the same resistance at each of the primary conductors and does not affect or destroy the balance of the system. Instead, the only result is a reduction in the primary current in the system.

This system also has the same advantages of increased potential of the differential transformers as a result of the circuit arrangement as is possessed in the Fig. 1 embodiment.

The specific construction of differential transformer may take any of a number of different forms. As shown in l and 2, only a diarammatic showing of the construction of transformer is incorporated. In Figs. 3, 4 and 5, specific structural representations which the (lif ferential transformers may take are shown.

The embodiment of the invention illustrated in Fig. 3 is shown connected electrically with leads in the manner shown for differential tran ier it! in Fig. 1. In this construction an E-shaped magnetizable member 55 having arms l? and 78 extending therefrom in substantially parallel equispaced relation, provides the means for mounting the windings ll, I12 and i3 which are shown in the nature of coils. These coils are mounted in substantial registration with one another, with the coil H on arm it, the coil 52 on arm 58, and the secondary coil winding on the arm TI, which is positioned intermediate the length of the frame member ?5. The conductor I4 is connected to the coil 5 l, the conductor 15 is connected to the coil i2, and the conductor it connects the two coils, and lead 57 is tapped to the lead I 5 at it and extends to the secondary winding 43. The conductor 19 is connected with the secondary winding 52 and cooperates with the conductors l4 and it? to complete the three- Wire transmission system. In this form the movable magnetic member takes the form of a bar 19 elongated and pivoted at its center at adjacent to the tip of the central arm "if. The bar '49 is adapted to swing about the pivot 29 so that one end thereof is spaced from one of the outermost arms "it, it a distance greater than the other end thereof is spaced from the other of said frame members 16, '18. The magnetic member 19 is here shown as in its neutral position.

In the embodiment of the invention shown in Fig. 4: the parts are again shown with the same connections and bearing the same identifying members as those in the diirerential transformer 58 of Fig. 1. This construction is characterized by a magnetic frame member which is formed in two parts, the two parts being fixedly related to one another, but being shiitable as a unit with respect to the third part. Thus an H-shaped frame is provided, having side members 85 and 86 and a central connecting bar 87. Ehe primary windings H and it are in the nature of coils mounted symmetrically upon the member 86 at opposite sides of the crossbar ill. Secondary winding 13 is shown in the nature of a coil mounted substantially centrally upon the crossbar Bl. The various leads and electrical connections are the same as those discussed previously and bear the same reference numerals. The bar 88 or" the frame extends substantially parallel to the crossbar 3? with its opposite ends equispaced from the adjacent end portions of the arms 95 and 85 of the H-shaped frame part. In this embodiment of the invention the lower ends of the frame parts 85 and 8t constitute the sensing members for the purpose of sensing the spacing of their tips from the uppermost surface of a magnetizable member or plate 89, upon which a non-magnetisable sheet 9c, such as a sheet of glass, is supported, the thickness of which is to be determined and compared to the spacing of parts 85 and 86 from the part 88. In the use of this device, since the various coils or windings H, l2 and i3 remain in stationary relation to each other and to the bar 88, the only variation which occurs and which is subject to measurement is the spacing between the parts 85 and 86, on the one hand, and the member 89 on the other hand, as determined by the thickness of the glass 94'! whose thickness is to be measured. As variations in the thickness of the glass 90 occur, the spacing between the parts 85, $6 and 89 varies and the measurement is secured, which is transmitted through the transmission lines it, ill and it; to the secondary differential transformer 21 and the follow-up mechanism of the device.

The third form of differential transformer is shown in Fig. 5, wherein a frame member constitutes an arcuate portion 95 from which project in radial relation to one another outer arms 98 and Ell at opposite ends thereof which serve to mount the primary windings H and I2. Equispaced from and equiangularly related to the arms 9? and Bl is another fixed arm Q8 upon which the secondary winding E3 of the transformer is mounted. The movable magnetic member constitutes an arcuate member 99 mounted upon an arm ltd rotatable about the center member ml which is concentric with the arcuate member 95. In this arrangement the member $9 is equispaced from the tips of each of the frame members 9t, 91 and 93 in all rotative positions thereof, but is of such a length that it normally acts upon a portion only of the tips of the frame members at and 9'5 magnetically considered. Consequently, as the member 99 is swung in either direction about its axis, an increased magnetic coupling occurs in the direction toward which it is swung, and a decreased magnetic coupling occurs in the opposite direction.

t will be understood that the forms of difierential transformers which are illustrated in Figs. 3, 4 and are all well adapted or suited for use in the systems shown in Figs. 1 and 2. It will also be understood that the form of diflerential transformers in Figs. 3, 4 and 5 are illustrative only of the types of transformers which may be used in this system, and it is not intended that use of these transformers must be made in this system. In other words, any other form or construction of differential transformer possessing two primaries of equal impedance but not necessarily of the same physical shape, a secondary and a movable magnetic member whose magnetic relation with the secondary remains essentially conbut whose magnetic relations with the two primaries are subject to variation in opposite sense upon movement thereof, may be employed in this system.

While the preferred embodiments of the invention have been illustrated and described herein, it will be understood that changes in the construction may be made within the scope of the appended claims without departing from the spirit of the invention.

I claim:

1. An electrical system for remote transmission of mechanical movements, comprising a transmitter, a receiver, said transmitter and receiver being similar and each including two primary windings, a secondary winding and a movable r agnetic member, the primary windings being connected with a power source by two conductors in series loop arran ement, the secondary windings being connected in series with each other a third conductor connecting a mid-point be tween the primary windings or the transmitter and a mid-point of the potential of the power source, means sensitive to the current in said th rd conductor, and means responsive to said current sensing means for shifting the movable magnetic member of said receiver.

2. An electrical system for remote transmission of mechanical movements comprising a transl litter, a receiver, means for sensing electrical unbalance between said transmitter and receiver, means responsive to said sensing means for actuating said receiver in a rebalancing sense, each or" said transmitter and receiver having two primary windings, a secondary winding, and a movable magnetic member having a variable magnetic reaction upon said primary windings, a pair of conductors connected to a power source and to each other at a midpoint, each conductor having one primary winding of each or said transmitter and receiver interposed therein and a third conductor connected at said midpoint and at a point of midpotential at said source, said secondary windings being connected in series in said third conductor.

3. A system as defined in claim 2, wherein a resistance containing lead is connected across said first conductors adjacent said source and said third conductor is connected to said last named lead at a point of midpotential.

i. A system as defined in claim 2, wherein a pair of similar resistors are connected in series across said first conductors adjacent to said source and said third conductor is connected be tween said resistors.

5. A s stem as defined in claim 2, wherein a lead connects said first conductors adjacent said source and has a variable resistor interposed therein, said resistor having a slider with which said third conductor is connected.

6. A system as defined in claim 2, wherein said sensing means constitutes an amplifier and said receiver actuating means is directionally responsive to the phase of the output of said amplifier.

7. An electrical system for remote transmission of mechanical movements comprising a transmitting differential transformer, a receiving differential transformer, said transformers being similar and each having two primary windings, a secondary winding and a movable magnetic member, a sensing member responsive to electrical unbalance, a rebalancing member responsive to said sensing member for adjusting the movable magnetic member of said receiving transformer, and three conductors connecting said transformers to each other and to a power source, one conductor having said secondary windings and sensing member connected in series therein, the other conductors each having a primary winding of each transformer connected in series therein and being connected to the opposite ends of said first conductor at points thereof at which the potential thereof is equal.

8. An electrical system as defined in claim 7, wherein said differential transformers have a normal balanced position and a normal rate of voltage induction in the secondary winding thereof, and wherein movement of said magnetic member from balanced position varies the impedances of said primary windings to vary the voltages thereof and adds the difference between said primary voltages to said normally induced secondary voltage.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,363,690 Razek Nov. 28, 1944 2,420,539 Hornfeck May 13, 1947 2,519,562 Glass et a1 Aug. 22, 1950 2,558,708 Macglorge June 26, 1951 2,568,588 Macglorge Sept. 18, 1951 2,615,936 Glass Oct. 28, 1952 

